Circuits presently and historically constructed and used for the purposes of voltage detection suffer from various conditions that limit their accuracy, and/or their flexibility, thereby compromising the circuit's efficacy for its intended purpose. FIG. 1 shows a circuit diagram of one embodiment of the negative voltage VBB (VBN) level sensor circuit disclosed in International Application Publication No. WO2003/094235. An N-channel MOSFET Q172, in which a constant voltage VREF is applied between the gate and the source, generates a constant current and based on this constant current, a current mirror circuit generates a current i101 that serves as a reference. A plurality of N-channel MOSFETs is serially-coupled to a current path to supply a substrate voltage VBB. The plurality of series MOSFETs are provided with a control terminal used for controlling process variations in the device. Concretely, when the substrate voltage VBB stated above is −1.0 (V), a trimming operation is performed such that the current i102 flowing in the series MOSFETs is balanced against the current i101. The balance between the current i102 flowing in the MOSFET Q176 and the current i101 is adjusted such that the source potential of the MOSFET Q176 coincides with the ground potential VSS.
The prior art technique shown in FIG. 1, however, presents the problem that the detected potential of the substrate voltage VBB may deviate owing to variations in the threshold voltage and NMOS characteristics (e.g., temperature) and therefore the substrate voltage VBB cannot be accurately adjusted to a target value.
Further, the prior art technique shown in FIG. 1 detects the current i101 generated from the constant voltage VREF and does not have the function of detecting the constant voltage VREF. Since the target value for the substrate voltage VBB is dependent on the circuit configuration and therefore cannot be determined by the constant voltage VREF, the substrate voltage VBB cannot be controlled in correspondence with the constant voltage VREF and therefore the degree of freedom for setting the substrate voltage VBB disadvantageously decreases.